Nanosize titanium dioxide may have damaging effects on brain cells, according to a study by Thomas Long, University of North Carolina, Chapel Hill, et al.

The study, conducted in conjunction with the Environmental Protection Agency and published online June 7 in Environmental Science & Technology, examined the effects of nanosize titanium dioxide on "biological targets that are sensitive to oxidative stress damage" such as the brain.

Titanium dioxide nanoparticles were a "reasonable candidate for study" because of their use in consumer products such as sunscreens, toothpaste and cosmetics, the researchers state.

"Such widespread use and its potential entry through dermal, ingestion and inhalation routes suggest that nanosize TiO2 poses considerable exposure risk to humans," they add.

While in vitro studies have addressed OS-mediated toxicity in other cell types, such as human colon cells, epithelia and skin fibroblast, potential neurotoxicity of TiO2 in culture has not been examined, the study notes.

In the trial, brain microglia (BV2) were exposed to a physico-chemically characterized nanomaterial called Degrussa P25.

Oxidative stress in the central nervous system is mediated by microglia, which react to potentially harmful stimuli by releasing an "oxidative burst," which includes "cytoplasmic engulfment" of the substances, the study explains. The activation leads to production of superoxide anions, which convert to reactive oxygen species. The excess of superoxide anions can diffuse from the microglial plasma membrane where they may damage other cells, such as neurons.

Data showed that nanosize TiO2 "stimulate microglia to produce ROS through the oxidative burst and through interference with the mitochondrial" energy production, which also can generate superoxide anions, according to Long et al.

"Transmission electron microscopy indicated that small groups of nanosized particles and micron-sized aggregates were engulfed by the microglia and sequestered as intracytoplasmic aggregates" after six and 18 hours of exposure.

"Whether the microglia's release of ROS translates into neuronal damage in situ is not addressed in this study, but pilot data indicate P25 stimulates apoptotic pathways in cultured neurons at concentrations" greater than 20 ppm after 24 hours of exposure, the study notes.

The researchers add that studies will be needed to determine the causal relationship between the surface charge of nanoparticles and OS-mediated events in neurons and other cells. Such an assessment would help scientists "better understand how the physical properties of particles interact and activate biological systems," they state.

Nanotechnology has generated increasing attention from regulatory authorities in the U.S. and Europe in recent years, particularly because little data exist on their ability to penetrate the skin and their potentially toxic effects in humans.

In the U.S., the National Toxicology Program formed a Nanotechnology Working Group to prioritize research needs based on the likelihood and magnitude of human exposure to the substances.

In May, a coalition of U.S. public interest groups filed a citizen petition requesting that FDA amend the OTC final sunscreen monograph to specify that products containing engineered nanoparticles be designated "new drugs" based on "insufficient" health and safety testing (¹ Also see "Nanomaterial Sunscreens Should Be Designated “New Drugs” – Petition" - Pink Sheet, 22 May, 2006., p. 13).

Overseas, the Commission of the European Communities developed an action plan on nanosciences and nanotechnologies for 2005-2009, which includes toxicological and ecotoxicological studies on the impact of nanoparticles on people and the environment.

In addition, the European Commission Health & Consumer Protection Directorate General announced in October it was seeking comments on risk assessment methods for nanotechnology. The consultation stemmed from an EC Scientific Committee on Emerging and Newly Identified Health Risks opinion on the status of nanotech risk assessment methodologies.

- Brooke McManus

Nanosize Sunscreen Ingredient Linked To Brain Stress In EPA Study

More from Archive

More from Pink Sheet